sedimentary

Ironstone Concretion / Goethite-Hematite Nodule

Goethite/Hematite (α-FeO(OH) / Fe2O3)

AI-generated identification · may be incorrect

Hardness: 5.0–6.5; Color: Rusty brown, dark reddish-brown, or black; Luster: Dull, earthy to sub-metallic; Structure: Often concretionary or botryoidal; Gravity: 3.3–4.3

Hardness: 5
Color: Rusty brown, dark reddish-brown, or black
Luster: Dull, earthy to sub-metallic

Identified April 12, 2026More sedimentary →

Explore Ironstone Concretion / Goethite-Hematite Nodule in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 5.0–6.5; Color: Rusty brown, dark reddish-brown, or black; Luster: Dull, earthy to sub-metallic; Structure: Often concretionary or botryoidal; Gravity: 3.3–4.3

Formation & geological history

Formed through the precipitation of iron-rich minerals from groundwater within sedimentary rock layers, often as secondary mineralization. These can range from modern formations to hundreds of millions of years old.

Uses & applications

Primarily used as an ore of iron in large deposits. For individual collectors, they are kept as curiosities, lapidary material, or naturally occurring 'charms'. Redder Varieties provide natural ochre pigments.

Geological facts

Many naturally occurring ironstone nodules are mistaken for meteorites because of their high density and dark, weathered appearance. They are sometimes called 'blueberries' when found in small, spherical forms on Mars.

Field identification & locations

Identify by its high density relative to other rocks, a reddish-brown streak test on unglazed porcelain, and its presence in gravel beds or creek bottoms. Often found in proximity to sandstone and shale.